If you want to terminate task execution in case of a parent task fail, right-click on an event or a task and select the Terminate execution if parent task failed command in the Add task menu. In this case none of the scheduled subtasks will be executed.

If a parent task is executed with an error, the task sequence shall be terminated. But if you wish to continue the execution of the task sequence, tick the Execution will continue if the parent task fails option available on the right part of the window.